In response to the increasing prevalence of antibiotic resistance in pathogenic bacteria, the pharmacokinetic properties and safety profiles of many novel antimicrobial peptides have been investigated. Bacteriocins are natural proteinaceous antimicrobial compounds produced by bacteria and active against taxonomically related bacteria (Klaenhammer, 1993). Species that produce bacteriocins have been studied extensively in the hope of finding safe and efficient means of inhibiting the growth of pathogenic bacteria, especially in foods (Cleveland et al. 2001). Bacteriocins produced by Gram-positive staining bacteria, such as lactic acid bacteria, have become a focus of interest as alternatives to conventional antibiotics (Nes et al. 1996). Nisin, the first bacteriocin ever isolated and now widely used as a food additive, was approved by the World Health Organization for use as a food preservative in 1973. This peptide is generally inactive against Gram-negative staining bacteria, imposing a limitation on its effectiveness when major food-borne pathogens such as Escherichia coli, Salmonella and Yersinia are involved (Du and Shen 1999; Zheng et al. 1999). Davies et al. (1998) reported that nisin produced by Lactococcus lactis was thermostable and remained active after treatment at 121° C. for 15 min at pH 3. Nisin is about 4.4 kDa and is stabilized by disulfide bonds.
Polymyxins, a class of antimicrobial agents, are synthesized by a non-ribosomal process. The peptide-synthase directed condensation reactions by which polymyxins are formed in the cell cytoplasm have been reviewed (Marahiel et al. 1997) and their biosynthesis in a cell-free enzyme system reported (Komura et al. 1985).
Many species within the genus Paenibacillus produce variants of polymyxins, which are generally composed of a cyclic decapeptide with a terminal fatty acid moiety (Martin et al. 2003). Five chemically distinct compounds, polymyxins A to E, differing in amino acid and fatty acid composition have been identified to date. Martin et al. (2003) reported that mattacin activity (800 AU ml−1) produced by P. kobensis M was maximal at 12 h of fermentation. Martin et al. (2003) also reported that mattacin and polymyxin B inhibited all Gram-negative staining species tested including E. coli O157:H7, Salmonella enterica serovar Rubislaw and Vibrio parahemeolyticus G1-166 but both failed to inhibit strains of Listeria and Bacillus. 
DeCrescenzo et al. (2007) isolated a new Paenibacillus species (P. amylolyticus C27) that produces polymyxins E1 and E2 (colistin A and B). The new antimicrobial peptides were reported to be effective against Gram-negative staining bacteria such as E. coli, Pseudomonas, Salmonella, and Shigella. DeCrescenzo et al. (2007) also reported that polymyxin E produced by P. amylolyticus C27 inhibited Gram-positive staining bacteria such as Staphylococus aureus ATCC 6538, Enterococcus faecalis ATCC 19433 and Streptococcus pyogenes ATCC 19165.
Zengguo et al. (2007) reported the co-production of polymyxin and lantibiotic by natural isolates of P. polymyxa. The two antimicrobial peptides were reported to display potent activity against many Gram-negative staining bacteria, including E. coli, Pseudomonas aeruginosa and Acinetobacter baumannii, and against Gram-positive food-borne pathogenic bacteria. Zengguo et al. (2007) also reported that polymyxin produced by P. polymyxa OSY-DF is stable from pH 2.0 to 9.0 and retained its activity after a short autoclaving.
Svetoch et al. (2005) reported the isolation of a new class IIa bacteriocin from P. polymyxa NRRL-B-30509, which has been used for the control of Campylobacter in poultry.
Among antimicrobial substances produced by Bacillus polymyxa are polymyxins, which are cyclic peptides with a long hydrophobic tail. Colistin is a polymyxin antibiotic discovered in the late 1940s for the treatment of Gram-negative infections. After several years of clinical use, colistin was associated with significant nephrotoxicity and neurotoxicty (Lim et al. 2010), rendering its use questionable. Colistin has a bactericidal effect against Gram-negative bacteria and acts as a detergent-like molecule (Landman et al. 2008). Recently, its application has returned as the last resort against multidrug-resistant organisms including Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae (Falagas and Kasiakou 2005).
The need for antibiotics with activity against these multidrug-resistant Gram-negative pathogens is urgent and in the absence of viable alternatives, clinicians now recommend colistin treatment when confronted with some multidrug resistant bacterial infections (Lim et al. 2010). This has led to the development of less toxic colistin molecules (Jian Li et al. 2004; Falagas et al., 2006). Colistin formulations available for clinical uses are colistin sulfate (for topical use) and colistin methane sulfonate for parenteral and aerosol therapy (Jian Li et al. 2006).
The coproduction of polymyxin E1 and a lantibiotic has been reported for P. polymyxa OSY-DF; a strain isolated from food (He et al. 2007). Polymyxin E1 was active against Gram-negative bacteria, whilst paenibacillin, a proteinaceous compound, exhibited activity against Gram-positive bacteria (He et al. 2007 & 2008). P. kobensis M isolated from soil produced mattacin (polymixin M) (Nathaniel et al. 2003) and Bacillus sp. strain B-60 produced various inhibitory molecules named sattabacin, hydroxysattabacin, sattazolin and methylsattazolin, with antiviral activity against herpes simplex viruses types 1 and 2 (HSV1 and HSV2) (Lampis et al. 1995). Strains of P. polymyxa have been isolated from different ecological niches including food matrices such as butternut squash, potatoes, rice, and wheat flour (Fangio et al. 2010).
Usually, E. coli is regarded as an inoffensive and common bacterium of the gastrointestinal tract of ruminants. The emergence of the enterohemorrhagic strain O157:H7 has become a major public concern worldwide. Indeed this pathogen is able to produce potent endotoxins with severe damage to the lining of the intestine, in particular in humans, allowing the strain to invade the body and infect organs such as the kidneys, sometimes with fatal consequences.
Spore-forming species such as Paenibacillus or other probiotic bacteria are known in the art. Andersson et al. (1997) showed that Bacillus cereus produced spores able to adhere to Caco-2 cell monolayers and to germinate in an environment similar to that of the small intestine and noted that the hydrophobicity of the spore is a contributing factor to adhesion. Angioi et al. (1995) evaluated the capacity of Bacillus subtilis strains to colonise the surface of Caco-2 cells, testing the bacteria both in the spore state and following stimulation of germination by exposure to low pH (as under gastric conditions) or to high temperatures. The degree of adhesion was found to vary in relation to the different physiological phases of the bacterial cells. Doyle et al. (1984) showed that spores or cells from several Bacillus species displayed a strong affinity for hexadecane and other hydrophobic solvents. Treatment of Bacillus spore suspensions with strong denaturants promoted their adherence to hexadecane (Koshikawa et al. 1989).